1. Field of the Invention
The present invention relates to an accelerated thermal process by pressure cooking for the production of nixtamalized corn flour and, more particularly, it relates to a process involving continuous precooking of the corn under pressure and moist conditions with the use of a lime solution. The process is advantageously applied to the production of instant masa flour for the preparation of tortilla, snack foods and the like.
2. Description of Related Art
Nixtamalized corn flour (NCF) is conventionally produced by alkaline cooking of food-grade corn under atmospheric pressure, steeping and washing, grinding the partially cooked corn (nixtamal) and drying to give corn masa flour. This flour is sieved and blended for different food product applications and it is usually supplemented with food-grade additives before packaging for commercial table tortilla and snack production. Montemayor and Rubio (Sustain, 1997) described both batch and continuous processes for cooking corn to produce instant masa flour. In the modern continuous process, the lime used is from 0.6 to 1% by weight (based on corn) and mixed with equal parts of corn and potable water. The corn suspension is cooked by atmospheric steam injection (Bressani, 1990) and although the pericarp is partially removed during cooking and washing, there is still some fiber left from the corn (with an estimated 7 to 9% dry solid loss).
The traditional method of cooking maize with lime (1-2% by weight) at the rural level is time consuming (around 14 to 15 hours) and requires hard labor. From 70% to 80% of the time is taken by the cooking and steeping-washing operations (with a 1:3 corn to water ratio); that time can be decreased to 8-12 hours or less at the urban or cottage level (with a 11 to 13% dry matter loss; Bressani, 1990).
At the industrial or commercial level, the xe2x80x9cgrinding and dehydrationxe2x80x9d steps are major cost factors. In any case, the availability of an instant flour has many advantages such as convenience for the customer, less labor, lower water and energy use, a safe and stable product (3 to 4 months under normal conditions), and the possibility to use the corn flour as a carrier of a macronutrients (defatted soybean flour or wheat and amaranth flour) and micronutrients (amino acids, vitamins and minerals).
Corn and tortilla chips are the second most popular salted snack food in the USA, after potato chips. However, the new or expanding plants along the US-Mexico border, including the new sewage treatment plants in northern Mexico, have to comply with the environmental regulations imposed by the NAFTA agreement. Any method which may decrease both time and cost, and still yield an acceptable nixtamalized corn dough or masa flour product per kilogram or raw corn, would be advantageous to the final customer. The mature dent corn kernel (Watson, 1987) has four separable components, on a dry weight basis: tip cap (0.8-1.1%), pericarp or hull (5.1-5.7%),endosperm (81.1-83.5%) and germ (10.2-11.9%).
In this connection, reference is made to the following U.S. Pat. Nos: 4,513,018; 4,594,260 and 5,532,013. These prior art methods for the industrial production of masa flour involve accelerated cooking with reduced amounts of water along with short processing times as well as low energy requirements for a high yield of the end product; however an industrial process capable of making such a masa flour having a low-cost wastewater treatment was still unavailable in the market at the time of the present invention.
Having in mind the disadvantages of the prior art methods, several studies were conducted to improve the efficiency of the water consumption during the alkaline-cooking and steeping-washing operations. For example, Anderson, in U.S. Pat. No. 3,083,103, describes a method for preparing a corn masa dough suitable for deep-fat frying including the steps of cooking corn in calcium hydroxide under high pressure, steeping the processed kernel for at least 30 to 120 minutes, and metal grinding the steeped kernel thereby to form said dough. Cooking comprises heating the kernel in a supersaturated solution of aqueous lime (1.5% by weight of corn) at a pressure ranging from 5 to 25 psig for 5 to 40 minutes. The corn chip thus obtained has a new, unique limed flavor and a highly desirable short texture.
Rubio in U.S. Pat. No. 4,250,802, discloses another improved method and apparatus for processing corn into masa flour and dough for tortilla products. His invention includes a dry-preheating of corn (at 135xc2x0 to 150xc2x0 C. for 12 to 18 minutes), quenching the cracked corn in lime-water for 5-15 minutes, and to stabilize the moisture content for grinding, drying, separating the flour into particle size categories, mixing the flour into dough and completing the cooking of the dough with a hot-lime solution under controlled temperature, and forming the cooked and extruded dough into the desired end product such as chip, taco shell, tortilla or the like.
Although the above described prior art methods can be useful in producing an increased yield of nixtamalized corn dough with a low-cost drying and dry solid losses as well, a continuous process was still unavailable for the expanding masa flour market for the tortilla and snack industry.
Accordingly, the present invention provides a method for continuous production of nixtamalized corn flour using pressure cooking, which generates not only a minimum amount of wastewater and solid loss, but also a high yield of the product.
Another object of the invention is to provide an instant masa flour for tortilla and derivatives thereof wherein such flour is uniform and homogenous in its physicochemical and rheological properties.
The above and other objects and advantages of the invention are achieve through a continuous process and apparatus applied to the production of partially-dehulled masa flour or instant masa flour, embodiments of which include pressure precooking with a lime solution so as to effect corn hull hydrolysis and partial cooking, reduced washing of precooked kernel and reduced corn loss, stabilizing the moisture content to a desired optimum level for grinding, grinding and drying the preconditioned kernel to produce a uniform partial cooking, cooling and drying the dry-ground particle, separating and recovering the fine grind so produced from the coarse grind while the latter is further aspirated to remove a hull fraction as corn waste, and regrinding the isolated coarse grind and further sieving it to obtain an instant masa flour for tortilla and snack.